Each etrv controls a radiator valve to regulate the heating in the room based on timed programmes set temperatures using the etrv improves your comfort and saves energy the benefit of having etrvs is that it enables you to control each radiator or room individually rather than heating your whole house from a single thermostat therefore you only heat the bedroom when it is in use which is likely to be at a differnet time to the lounge or sitting room by only heating the rooms you are in yo